refactor(core): share keyframe property defaults between SDK and Studio (#5438)

Move the keyframe rest-value table into @hyperframes/core/keyframe-defaults
and import it from the SDK backfill and Studio's gsapShared, replacing the two
hand-synced copies.

Closes #5387

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/package-subpaths.json

@@ -86,6 +86,12 @@
       "types": "./dist/studioPreviewMark.d.ts",
       "environments": ["browser", "bun", "node"]
     },
+    "./keyframe-defaults": {
+      "source": "./src/keyframeDefaults.ts",
+      "runtime": "./dist/keyframeDefaults.js",
+      "types": "./dist/keyframeDefaults.d.ts",
+      "environments": ["browser", "bun", "node"]
+    },
     "./gsap-cdn": {
       "source": "./src/gsapCdn.ts",
       "runtime": "./dist/gsapCdn.js",

packages/core/package.json

@@ -98,6 +98,12 @@
       "import": "./src/studioPreviewMark.ts",
       "types": "./src/studioPreviewMark.ts"
     },
+    "./keyframe-defaults": {
+      "bun": "./src/keyframeDefaults.ts",
+      "node": "./dist/keyframeDefaults.js",
+      "import": "./src/keyframeDefaults.ts",
+      "types": "./src/keyframeDefaults.ts"
+    },
     "./gsap-cdn": {
       "bun": "./src/gsapCdn.ts",
       "node": "./dist/gsapCdn.js",
@@ -578,6 +584,10 @@
         "import": "./dist/studioPreviewMark.js",
         "types": "./dist/studioPreviewMark.d.ts"
       },
+      "./keyframe-defaults": {
+        "import": "./dist/keyframeDefaults.js",
+        "types": "./dist/keyframeDefaults.d.ts"
+      },
       "./gsap-cdn": {
         "import": "./dist/gsapCdn.js",
         "types": "./dist/gsapCdn.d.ts"

packages/core/src/keyframeDefaults.test.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vitest";
+import { KEYFRAME_PROPERTY_DEFAULTS } from "./keyframeDefaults";
+
+describe("KEYFRAME_PROPERTY_DEFAULTS", () => {
+  it("holds the rest value of each numeric keyframe prop", () => {
+    expect(KEYFRAME_PROPERTY_DEFAULTS).toEqual({
+      opacity: 1,
+      x: 0,
+      y: 0,
+      scale: 1,
+      scaleX: 1,
+      scaleY: 1,
+      rotation: 0,
+      width: 100,
+      height: 100,
+    });
+  });
+
+  it.each(["color", "filter", "backgroundColor"])("has no default for %s", (prop) => {
+    expect(KEYFRAME_PROPERTY_DEFAULTS[prop]).toBeUndefined();
+  });
+});

packages/core/src/keyframeDefaults.ts

@@ -0,0 +1,12 @@
+// A prop absent here has no safe static default; each caller decides how to treat it.
+export const KEYFRAME_PROPERTY_DEFAULTS: Readonly<Record<string, number>> = {
+  opacity: 1,
+  x: 0,
+  y: 0,
+  scale: 1,
+  scaleX: 1,
+  scaleY: 1,
+  rotation: 0,
+  width: 100,
+  height: 100,
+};

packages/sdk/src/engine/keyframeBackfill.ts

@@ -12,25 +12,7 @@
  * keyframes (GSAP reads the rest value from the DOM), matching recast (which skips
  * any prop whose default is null).
  */
-
-// Numeric rest values for editable transform/style props. Props absent here have
-// no safe static default and are intentionally omitted from the backfill set.
-//
-// KEEP IN SYNC WITH packages/studio/src/hooks/gsapShared.ts:PROPERTY_DEFAULTS —
-// the studio (recast) and SDK (acorn) paths must derive the same defaults or
-// SDK-written keyframes drift from server-written ones (the exact bug this fixes).
-// TODO: lift the canonical table into @hyperframes/core and import from both.
-const KEYFRAME_PROPERTY_DEFAULTS: Record<string, number> = {
-  opacity: 1,
-  x: 0,
-  y: 0,
-  scale: 1,
-  scaleX: 1,
-  scaleY: 1,
-  rotation: 0,
-  width: 100,
-  height: 100,
-};
+import { KEYFRAME_PROPERTY_DEFAULTS } from "@hyperframes/core/keyframe-defaults";
 
 /** Derive the backfillDefaults for an add-keyframe op (numeric-default props only). */
 export function deriveKeyframeBackfillDefaults(

packages/studio/src/hooks/gsapShared.ts

@@ -25,17 +25,7 @@ export interface IframeGsap {
 
 // ── Constants ─────────────────────────────────────────────────────────────────
 
-export const PROPERTY_DEFAULTS: Record<string, number> = {
-  opacity: 1,
-  x: 0,
-  y: 0,
-  scale: 1,
-  scaleX: 1,
-  scaleY: 1,
-  rotation: 0,
-  width: 100,
-  height: 100,
-};
+export { KEYFRAME_PROPERTY_DEFAULTS as PROPERTY_DEFAULTS } from "@hyperframes/core/keyframe-defaults";
 
 /** A tween's eases for re-writing it as keyframes: a flat tween's ease must become easeEach,
  *  since GSAP eases each percentage segment power1.inOut whatever the tween-level ease says. */